Reducing the File Size of Adobe Lightroom Previews

To change the preview cache settings, go to File/Catalog Settings, File Handling tab. Set the Standard Preview Size to the width of your largest monitor, and set Preview Quality to Low (assuming disk space is your major concern).

Set the “Automatically Discard 1:1 Previews” to taste, depending on your working habits. If you rarely work on a single image for more than a week, then set it to a week.

If you work at zoom level “Fill” and with the panels hidden a lot, this might turn out to be a little small, and you may wish to increment the preview size. You’ll know if this is the case, as Lightroom will display a bezel with something like “rendering larger preview”.

To delete the preview file, exit out of Lightroom and then just literally delete the preview file (not the catalog file!) from the Lightroom folder.

Lightroom will rebuild the previews as it needs them according to those new settings, or you can rebuild them manually by selecting all and then choosing Library/Previews/Render Standard-Sized Previews. Warning — this will take a while for 3,000 images!